A tablet board is an example of a general external input unit. The tablet board, which is a type of a graph readout unit, reads coordinate values of X, Y with a light pen on the board and inputs the coordinate values into a computer, thereby being used for reading characters.
The conventional tablet board has a limitation in its transmission speed since a modem is used when giving and taking data through the tablet board. For example, when transmitting data by using the modem at a speed of 9600 BPS (Bit Per Second), a coordinate point of 100 Point Per Second is input on the tablet board. However, when a user draws with the light pen on the tablet board, he can draw a locus of more than 100 Point Per Second, and at that time, since a connecting line of the locus is broken at different places, the user has to connect the spaces.
Furthermore, in order to connect the discontinued spaces between the connection lines of the drawn locus, after reading coordinate points of both ends of the discounted space, the two coordinate points are to be linearly connected. In this regard, since such a connection in the prior art is to be handled by software, there is a disadvantage in that a processing speed is slow due to the limitation of a clock frequency.
Meanwhile, U.S. Pat. No. 4,988,984 describes an image interpolator for an image display system, and FIG. 1 shows a block diagram thereof.
The conventional image interpolator according to FIG. 1 interpolates an image by expanding the number of input pixels by an expansion coefficient and making pixels more than the number of originally input pixels, in which its purpose is to prevent a picture quality and definition from being deteriorated by providing a realtime image interpolation function.
The image interpolator comprises an input register 1000 for storing an interpolated image, a switch 1100 connected to the input register 1000, a number of line buffers 1200, 1300, 1400 connected to the switch 1100, a coefficient generator 1500 for generating an interpolation coefficient, an address generator 1600 for generating an address according to a signal from the coefficient generator 1500, a selector 1700 for selecting the outputs of the line buffers 1200, 1300, 1400 according to a controlling signal of the coefficient generator, and a second dimensional filter 1800 connected to the selector 1700 and coefficient generator 1500, for outputting the interpolated image value based on answering to the coefficient generator 1500 and contents of line buffers 1200, 1300, 1400.
A method of generating an interpolation signal from the conventional image interpolator with the above-mentioned construction is to make an interpolation signal Q (i, m) by the original input pixels P(i, j) and P(i, J+1), an interpolation signal Q (i+1, m) by P(i+1, j) and P (i+1, J+1), and an interpolation signal V(n, m) by Q (i, m) and Q (i+1, m), as shown in FIG. 2, thereby outputting V(n, m) as an interpolation signal and interpolating an image.
However, the conventional image interpolator generates an interpolation signal only by taking continuously an average value of input pixels. That is, since it interpolates an image by making an image interpolation signal according to an interpolation coefficient, the interpolation signal depends on the interpolation coefficient. Furthermore, since it must have a circuit for generating an interpolation coefficient, it has a disadvantage that the circuit is complicated.